Though dogs cannot relate to abstract human concepts such as minutes and hours, there is plenty of evidence that they can sense the passing of time. Sensory cues including light, temperature and odors throughout the day provide dogs a lot of information about time-sensitive events. For example, they may anticipate that it is time for a guardian to come home because the odor of that person has faded to the degree it always does right before that person returns. Their own sensations can be a factor, too—many dogs know it’s dinnertime because they are hungry, not because they know that it is 6 o’clock or that 10 hours have passed since breakfast.
Though an internal sense of time may play a role in canine behavior, it’s not always easy to eliminate sensory cues. One study showed that dogs greet their owners more enthusiastically after longer separations that after shorter ones. Two-hour absences led to more intense reunions than those of 30 minutes. It remains unknown if internal or external factors are affecting how dogs understand these time intervals.
Other species have a sense of time, too. In one study, cats were trained to go to different bowls for food when released from confinement based on how long they have been in the cage, and they were able to differentiate 5 seconds from 20 seconds and even from 10 seconds. The short time frame suggests that the cats were internally judging the time.
A recent study of mice may offer a new understanding of how mammalian brains keep track of such short intervals of time. (Though all species of animals are different, the similarities between us are immense.) Within mammals, the ways in which our brains and the rest of our nervous systems function are alike in many ways, which is why studies of one species often add insights into others.
For this particular study, mice were trained to run on a real treadmill in a virtual reality set-up. Halfway down a hallway scene, where the apparent texture of the floor changes, there is a door. The mice stop at the sight of the door, but after 6 seconds, the door opens and they resume running down the hallway to collect a food reward. In the test condition, the door is made invisible, but its location is still known by the mice because of the change in the flooring. Even when the door was invisible to the mice, they paused for 6 seconds and then continued to run along the hallway to the food reward. Using virtual reality eliminated all possibly sensory cues for the mice. Being unable to perceive the opening of the door, the mice based their behavior on their brain’s internal sense of time.
Using an advanced technique to generate high-resolution of the mice brains, the scientists who conducted the study observed the neurons in the brain fire. While mice were running, the neurons involved in spatial tasks were firing. When they stopped, those cells ceased to be active and a new group of cells that had not been firing became active. Those cells apparently encode how much time the mouse has been engaged in resting behavior.
These previously unknown neurons are in the medial entorhinal cortex of the brain, and they turn on and keep track of time when an animal is waiting for something. The research shows that mice have a physical representation of time in their brain that allows them to measure a time interval.
Further research will be required to determine if the same system is operating in the brains of additional species and hopefully scientists will conduct studies on dogs to determine if their brains keep track of time in this way. If dogs do so, it would be intriguing to explore how accurate the timekeeping is over various time periods and how much individual variation exists in the ability to track time.
In what situations have you seen behavior that makes you suspect your dog can keep track of time?